Photographic material containing antistatic coating

ABSTRACT

This application describes photographic material which comprises a support base, at least one photographic emulsion layer on at least one side of said base, the material being characterized in that it has an outer antistatic layer which consists of a dried gelled layer which comprises sodium cellulose sulphate, which has a high degree of substitution, and a potassium salt.

0 United States Patent [151 3,653,906 Wood 51 Apr. 4, 1972 1 PHOTOGRAPHIC MATERIAL References Cited CONTAINING ANTISTATIC COATING UNITED STATES PATENTS [72] Inventor: Henry Walter Wood, llford, England 2,725,297 11/1955 Morey ..96/87 3,437,484 4/1969 Nadeau ..96/87 [731 Asslgnee= England 2,476,240 7/1949 Famulener ..96/87 x [22] Filed: Sept. 29, 1969 Primary Examiner-Ronald H. Smith PP 862,057 Att0rneyCushman,Darby&Cushman [30] Foreign Application Priority Data [57] ABSTRACT Oct. 3, 1968 Great Britain ..47,039/68 h application describes photographic mat?rial which prises a support base, at least one photographic emulsion layer on at least one side of said base, the material being characterized in that it has an outer antistatic layer which consists of [58] Field of Search ..96/87 A, 67 a dned gelled layer whlch compnses sdmm sulphate, which has a high degree of substitution, and a potassium salt.

8 Claims, No Drawings This invention relates to photographic film material provided with an antistatic layer and to the production of such film material.

It is known that photographic film material exhibits a tendency to pick up electrostatic charges during the course of its manufacture and also when it is being processed. When an electrostatically charged film is discharged so called static marks are produced. These marks show as areas of local over-exposure on the developed film. It is possible to reduce the tendency of photographic film to pick up electrostatic charges by the provision of a layer which has a relatively high electroconductivity. Any electrostatic charge picked up by a film having such a layer rapidly leaks to earth without causing a discharge.

It is the object of the present invention to provide photographic material which comprises such a layer of relatively high conductivity.

According to the present invention, therefore, there is provided photographic material which comprises a support base having coated thereon on one or both sides at least one photographic emulsion layer, there being present on at least one topmost emulsion layer a dried gelled layer which comprises sodium cellulose sulphate, which has a high degree of substitution, and a potassium salt, or photographic material which comprises a support base which has on one side thereof at least one photographic emulsion layer and which has on the other side a dried gelled layer which comprises sodium cellulose sulphate, which has a high degree of substitution, and a potassium salt.

By sodium cellulose sulphate which has a high degree of substitution is meant sodium cellulose sulphate which has, on an average, at least two sulphate radicals per glucose unit in the cellulose chain.

The preferred potassium salt is potassium chloride and it is preferred that the gelled layer also comprises gelatin, the amount of gelatin present in the layer being not substantially greater than the amount of sodium cellulose sulphate.

According to another embodiment of the present invention there is provided a process for the production of photographic material which carries on at least one surface thereof a layer of relatively high conductivity, which process comprises coating on to the surface of the photographic material an aqueous solution which comprises from 1 to 5 percent by weight of sodium cellulose sulphate and from 0.5 percent to 2 percent by weight of a potassium salt and cooling the photographic material to leave a gelled layer on the coated surface and then drying the material.

The gelled layer which is formed when the material is cooled after coating comprises sodium cellulose sulphate, which has been gelled by the presence of the potassium salt in the aqueous solution, and the potassium salt.

It is preferred that the potassium salt is potassium chloride. Also it is preferred that from 0.2-2 percent by weight of gelatin is present in the aqueous solution.

When gelatin is also present in the aqueous solution the gelled layer comprises sodium cellulose sulphate, gelatin and the potassium salt. Such dried gelled layers which comprise gelatin are stronger than layers without gelatin and thus are able to form a better emulsion protective layer or supercoat.

lf substantially more gelatin than sodium cellulose sulphate is present in the gelled layer the conductivity of the layer drops and becomes insufficient to reduce the tendency of the photographic film to pick up electrostatic charges.

The presence of the potassium salt in the aqueous solution reduces the viscosity of aqueous solutions of sodium cellulose sulphate and causes the sodium cellulose sulphate to gel on cooling. Also the potassium salt reduces the viscosity of aqueous solutions which comprise sodium cellulose sulphate and gelatin.

A particularly useful aqueous solution for use in the present invention comprises 1 percent by weight sodium cellulose sulphate, 1 percent by weight gelatin and 1 percent by weight of potassium chloride. This solution has a comparatively low viscosity and thus can be coated onto the photographic material without difficulty. When the solution has been coated on to photographic material there is formed a strong protective coating on the photographic material after cooling and drying.

The following table shows the difference in viscosity of a 1 percent by weight aqueous solution of sodium cellulose sulphate in the presence and absence of gelatin and potassium chloride.

graphic silver halide emulsion layer was supercoated with an aqueous solution containing by weight 1 percent sodium cellu lose sulphate, 1 percent potassium chloride and 1 percent gelatin. The coating weight of each of the constituents of the layer thus applied was approximately 5mg/dm This will be termed film assembly B.

Another portion from the same strip, which will be designated A, had a supercoat deriving from a 2 percent solu' tion of gelatin, applied at a coating weight of approximately l5mg/dm Small amounts of normal spreading agents were present in both supercoat solutions.

The behavior of A, in the following tests, was virtually identical with that of an unsupercoated emulsion layer.

The film strips were brought to equilibrium at a relative humidity of 20 percent and their resistivity at this humidity level was measured under an applied potential of lOlcV. Results were as follows.

TABLE 11 log R (ohm/sq) The resistivity of the assembly with sodium cellulose sulphate in the supercoat was thus some two orders of magnitude less than that of the control.

ln another test, also carried out at 20 percent R.l-l., the propensity of the film strips to static formation was assessed. The strips were passed between rubber rollers to create a static charge which was measured by ajuxtaposed field meter. ln variants of this, the rollers were sleeved with other materi als to study the effect of the latter on charge production. Results given below indicate the field strength in v/cm of the induced electrostatic field.

The sign of the charge was positive in all cases. It can be seen that the supercoat containing sodium cellulose sulphate has reduced the propensity of the film strips to static formation in all cases.

The photographic properties of A and B either initially or after a period of incubation were identical. We claim as our invention:

1. Photographic material which comprises a support base, at least one photographic silver halide emulsion layer on at least one side of said base, the material being characterized in that it has an outer antistatic layer which consists of a dried gelled layer which comprises 1 to 5 parts by weight sodium cellulose sulphate having at least two sulphate radicals per glucose unit in the cellulose chain, 0.5 to 2 parts by weight of potassium chloride and 0 to 1 part by weight of gelatin.

2. Photographic material according to claim 1 wherein the photographic material has at least one photographic silver halide emulsion layer on one side only of the base and the antistatic layer is present as an outer layer on the topmost emulsion layer.

3. Photographic material according to claim 1 wherein the photographic material has at least one photographic silver halide emulsion layer on one side only of the base and the antistatic layer is present as an outer layer on the reverse side of the base.

4. Photographic material according to claim 1 wherein the photographic material has at least one photographic silver halide emulsion layer on each side of the base and the antistatic layer is present as an outer layer over at least one of the outermost photographic silver halide emulsion layers.

5. A process for the production of photographic material which carries on at least one surface thereof an antistatic layer, which process comprises coating on to a film base at least one layer of photographic silver halide emulsion, and coating on at least one outermost surface an aqueous solution which comprises from 1 to 5 percent by weight of sodium cellulose sulphate having at least two sulphate radicals per glucose unit in the cellulose chain, from 0.5 percent to 2 percent by weight of potassium chloride and from O to 2 percent by weight of gelatin and cooling the photographic material to leave a gelled layer on the said outermost surface and then drying the material.

6. A process according to claim 5 wherein 0.2-2 percent by weight of gelatin is present in the aqueous coating solution.

7. A process according to claim 6 wherein the aqueous coating solution comprises 1 percent by weight of sodium cellulose sulphate, 1 percent by weight of gelatin and 1 percent by weight of potassium chloride.

8. A process according to claim 5 wherein the solution comprises gelatin in an amount of which is not greater than the amount of sodium cellulose sulphate present. 

2. Photographic material according to claim 1 wherein the photographic material has at least one photographic silver halide emulsion layer on one side only of the base and the antistatic layer is present as an outer layer on the topmost emulsion layer.
 3. Photographic material according to claim 1 wherein the photographic material has at least one photographic silver halide emulsion layer on one side only of the base and the antistatic layer is present as an outer layer on the reverse side of the base.
 4. Photographic material according to claim 1 wherein the photographic material has at least one photographic silver halide emulsion layer on each side of the base and the antistatic layer is present as an outer layer over at least one of the outermost photographic silver halide emulsion layers.
 5. A process for the production of photographic material which carries on at least one surface thereof an antistatic layer, which process comprises coating on to a film base at least one layer of photographic silver halide emulsion, and coating on at least one outermost surface an aqueous solution which comprises from 1 to 5 percent by weight of sodium cellulose sulphate having at least two sulphate radicals per glucose unit in the cellulose chain, from 0.5 percent to 2 percent by weight of potassium chloride and from 0 to 2 percent by weight of gelatin and cooling the photographic material to leave a gelled layer on the said outermost surface and then drying the material.
 6. A process according to claim 5 wherein 0.2-2 percent by weight of gelatin is present in the aqueous coating solution.
 7. A process according to claim 6 wherein the aqueous coating solution comprises 1 percent by weight of sodium cellulose sulphate, 1 percent by weight of gelatin and 1 percent by weight of potassium chloride.
 8. A process according to claim 5 wherein the solution comprises gelatin in an amount of which is not greater than the amount of sodium cellulose sulphate present. 